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Large Dinosaurs Had a Nesting Strategy to Avoid Breaking Eggs

Oviaptorosaurs likely kept their eggs in open nests—more like bird than crocodiles—but needed to arrange their eggs carefully

(Louie Psihoyos/Corbis)
smithsonian.com

Given only the fossilized bones, traces of footprints left in muddy patches and occasional nest, scientists have had to make a lot of educated guesses about what dinosaurs were like. For a long time, no one was certain whether dinosaurs nested and cared for their young like birds and crocodiles do. Though we’re more certain now, traces of those past questions still linger, as with the name "oviraptorosaurs," Gretchen Vogel notes for Science

The name means “egg-thief lizards,” because researchers originally assumed the creatures ate the eggs that were so often found with them. But scientists now realize the animals were nesting, not feasting.

Some oviraptorosaurs were the size of a modern-day rhinoceros, which raises the question: How did they nest without breaking their eggs? Using the ancient evidence available, Kohei Tanaka of the University of Calgary in Canada thinks he has the answer. 

First, he compared the pores in fossilized oviraptorosaurus eggs to modern eggs. Birds, who use open nests, have less porous eggshells that keep water in, whereas crocodiles can lay eggs that breath more because they bury their nests. Tanaka’s results, presented at the Society of Vertebrate Paleontology annual meeting, show that oviraptorosaurus has less porous eggs and probably an open nest structure.

But that creates a problem. Vogel writes:

Tanaka then calculated how much weight the eggs could bear before they cracked. He found that the eggs of small and medium-sized oviraptorosaurs could have borne the weight of an adult sitting on a nest of a dozen or so tightly packed eggs. But the eggs of the largest animals would have broken.

The larger dinosaurs solved this by arranging their eggs in an open ring. This allowed the rhino-sized animals to rest most of their weight in the middle, open ground, while still keeping the ring of eggs warm. The work adds one more piece to our picture of what life might have been like for these intriguing creatures.

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